The reason I said Nakama and Friends separately, is because Luffy would consider Shanks to be his friend, or Law to be his friend, even though they're not Nakama, and are rival Pirate Crews.
Nakama is more like comerades than friends in Japan, from what I've seen. But, HELL, I've been wrong before. I think Luffy views his crew as Nakama, but still has friends he treasures just as much as his crew/Nakama.
Is there anyone here familiar with the original Japanese One Piece Manga, who can say if Luffy uses Nakama to refer to people outside the crew/people he's invited to the crew?